A fluid catalytic cracking (FCC) process aims to convert hydrocarbons with a high boiling point into lighter hydrocarbon fractions, such as gasoline and liquefied petroleum gas (LPG), inter alia.
Generally, the reactor used in a FCC process is of the tube type, with upward vertical flow, known in the technical literature as a riser type reactor. Such a reactor uses a solid catalyst consisting basically of a powder of fine particle size which, normally preheated, is introduced into the reactor. Upon entry into the reactor, in its lower portion, the catalyst is preaccelerated with vapor and intimately mixed with a preheated, sprayed hydrocarbon charge. After the so-called mixing region, the resulting mixture of vaporized hydrocarbon and catalyst continues to react, converting, during the upward vertical flow through the tube reactor, heavy hydrocarbon fractions with high boiling points into light hydrocarbon fractions with low boiling points.
As an alternative to the tube reactor with upward vertical flow, for converting heavy hydrocarbons into light hydrocarbon fractions, it is possible to use a tube reactor with downward vertical flow, also known in the technical literature as a downer or dropper type reactor.
A downer reactor offers certain technical and financial advantages when compared with the riser reactor, such as: increased conversion to products with greater added value, such as gasoline or liquefied petroleum gas, owing to the maintenance of a more intimate contact between the catalyst and the vaporized reagent charge during the downward vertical flow through the tube reactor; less generation of light gases, allowing a reduction in the gas-treatment and compression system; less generation of coke, giving rise to a reduction in the system for regeneration of the catalyst, in which the coke deposited during the passage of the catalyst through the tube reactor is burnt. The intimate mixing of the heavy hydrocarbon charge with a high boiling point with the catalyst at high temperature is a critical stage in the fluid catalytic cracking process. An intimate contact between the charge and the catalyst is very important in order to achieve satisfactory mixing and rapid vaporization thereof. Upon entry into the mixing region, the charge is sprayed in the form of small droplets by means of the use of injector inlets.
In tube reactors with upward vertical flow (risers), the production of an intimate mixture is promoted through the action of the force of gravity on the catalyst, leading to the occurrence of reflux of catalyst in the region where the hydrocarbon charge is injected. This does not occur in tube reactors with downward vertical flow, in which the force of gravity does not promote the existence of catalyst reflux in the charge-injection region. Therefore, in downer-type reactors, the production of a mixture which is as intimate and as homogeneous as possible, at the site where the catalyst encounters the hydrocarbon charge, is highly desirable.
After the stage of mixing the catalyst at high temperature with the sprayed heavy hydrocarbon charge, the resulting mixture continues to react throughout the flow through the tube reactor. During travel, it is important for the catalyst to continue to be mixed homogeneously and intimately with the hydrocarbon charge so as to allow the occurrence of catalytic cracking reactions in preference to thermal cracking reactions. It is in this stage that the downer-type reactor offers advantages over the rise-type reactor, by virtue of the fact that there is less segregation of the stream of catalyst from the stream of hydrocarbon. Thus, these characteristics prove that, for downer-type reactors, it is important to obtain the best mixture possible, which also depends on a homogeneous spatial distribution of the catalyst, even in the stage of supplying the catalyst.
This invention relates to an entry device for downer-type reactors which is designed to allow the occurrence of an intimate and homogeneous mixing of the catalyst, in the form of heated solid particles, with the sprayed hydrocarbon charge, giving rise to rapid vaporization of the charge. In addition, the device enhances maintenance of the homogeneity of the mixture, minimizing segregation between the charge and catalyst after the stream of fluid has left the mixing region and during its flow through a downward tube reactor.